1. Field of the Invention
The invention relates to the field of electronic devices, and in particular, to a method and structure for accurately and neatly assembling a memory card-type electronic apparatus.
2. Related Art
Memory cards are widely used, for example, for storing digital pictures captured by digital cameras. One useful format is the Secure-Digital (SD) format, which is an extension of the earlier MultiMediaCard (MMC) format. These and other similar card-like structures are collectively referred to herein as “memory cards”. Such memory cards are also useful as add-on memory cards for other devices, such as portable music players, personal digital assistants (PDAs), and even notebook computers. SD cards are hot-swappable, allowing the user to easily insert and remove SD cards without rebooting or cycling power. Since the SD cards are small, durable, and removable, data files can easily be transported among electronic devices by being copied to an SD card. SD cards are not limited to flash-memory cards, but other applications such as communications transceivers can be implemented as SD cards.
An important aspect of most memory card structures is that they meet size specifications for a given memory card type. In particular, the size of the casing or housing, and more particularly the width and thickness (height) of the casing/housing, must be precisely formed so that the memory card can be received within a corresponding slot (or other docking structure) formed on an associated card-hosting device. For example, using the SD card specifications mentioned above, each SD card must meet the specified 24 mm width and 2.1 mm thickness specifications in order to be usable in devices that support this SD card type. That is, if the width/thickness specifications of a memory card are too small or too large, then the card can either fail to make the necessary contact pad-to-card-hosting device connections, or fail to fit within the corresponding slot of the associated card-hosting device.
One conventional method for manufacturing memory cards that meet required size specifications includes using a cover or housing that is typically adhesively attached to the PCBA substrate over the semiconductor components. One shortcoming of this approach is that the thickness of such covers is necessarily relatively thick, and therefore takes up a significant amount of the specified memory card thickness (e.g., the 2.1 mm thickness of standard SD cards). As a result, the choice of memory device and other components mounted used in these memory cards is limited to devices that are relatively thin. In addition, because such covers are fabricated separately and then attached to the substrate using an adhesive, the use of such separate covers increases production and assembly costs, and the covers can become detached from the substrate. Another conventional method for manufacturing memory cards is to ultrasonically bond the upper and lower portions of the card assembly. However, tiny bond structures must be precisely made on adjoining portions and thus increases manufacturing cost. In either method mentioned above, there is always a concern about the quality of the bonding, and the joining seam between the two portions is typically the weakest area of the final assembly and is subject to premature separation, resulting in damages to the memory cards.
U.S. Pat. No. 6,462,273 discloses a second conventional memory card fabrication process that avoids the thickness problems associated with separate cover structures by forming a molded casing over the PCBA components. First, the PCBA is assembled using normal practices by forming individual module substrates that are connected to a common carrier by connecting segments, with the material used for the carrier and connecting segments being the same as that of the module substrate. Each module substrate is attached along its side to the carrier substrate by way of the connecting segments, with wide carrier segments of the carrier substrate between located between each adjacent pair of module substrates. During a subsequent plastic molding process, round shaped rods are utilized for forming notches on the card body at locations where the card body remains connected to the carrier by way of the connecting segments. Later, round shape cutters are used for cutting the connecting segments through the notched areas, thereby separating the molded memory cards from the carrier.
A problem with the manufacturing method disclosed in U.S. Pat. No. 6,462,273 is that the disclosed carrier impedes the efficient molding of several memory cards during a single molding cycle (i.e., simultaneously injecting plastic into several cavities of a multi-cavity mold) due to the large support sections separating adjacent card bodies. That is, each molding cavity of a multi-cavity mold assembly must be spaced apart by a distance corresponding to the wide carrier segments located between adjacent module substrates. This intervening space both increases tooling costs by requiring a larger mold, and decreases production efficiency by limiting the number of cavities that a given molding apparatus can support. Furthermore, handling of the small substrate wherein electronic components are mounted adds to the complication of manufacturing and substantially lowers the yield rate.
What is needed is a secured card-type electronic apparatus housing and assembly method that enables high production throughput by way of cost-efficient molding techniques that avoid the problems associated with conventional production methods.